This application relates generally to methods of forming electroactive ceramics by laser machining, and more particularly to methods of producing sensors and actuators having superior mechanical and electroactive properties.
Ceramic materials are brittle and are difficult and costly to form in arbitrary shapes. In particular, it would be desirable to form electroactive ceramics in more complicated shapes than those currently available.
Some methods of machining ceramics for a variety of reasons have been disclosed. For example, U.S. Pat. Nos. 4,131,484 to Caruso et al., 4,642,505 to Arvanitis, and 5,369,862 to Kotani et al. disclose using a laser to adjust the resonant frequency of a piezoelectric ceramic. U.S. Pat. Nos. 4,422,003, 5,615,466, 5,796,207, and 5,818,149, all to Safari et al., describe methods of producing polymer-ceramic piezoelectric composites. U.S. Pat. No. 4,650,619 to Watanabe describes a method of laser machining apertures in a ceramic member to create gas supply passages.
It is an object of the present invention to provide a method of machining electroactive ceramics which is relatively inexpensive, capable of producing complex shapes, and does not unduly compromise the electroactive properties of the electroactive ceramic. It is a further object of the present invention to provide sensors and actuators having flexibilities and anisotropic behaviors superior to those known in the art, as well as improved mechanical robustness and handling properties. It is still a further object of the present invention to provide sensors and actuators having shapes which allow superior electromechanical performance compared to those known in the art. It is yet a further object of the present invention to provide sensors and actuators which can be attached to electrodes in improved configurations.
The present invention achieves these and other objects by providing a method of machining electroactive ceramics for transducer applications. A Laser-Beam Machining (LBM) process is used to remove material selectively enable cuts, grooves and general forms for transduction. For example, a particularly useful form will be for surface strain relief of planar electroceramics. This introduces greater bending flexibility as well as directional or anisotropic coupling behavior in the material. Other example usages include relief patterns similar to those developed in silicon wafers for Micro ElectroMechanical Structures (MEMS). The LBM process includes through-cuts, grooves and other material removal from a ceramic substrate, and is not necessarily limited to planar structures. This process offers a cost-effective alternative for moderate to large-scale production of flexible, anisotropic sensors and actuators.
In one aspect, the invention includes a method of producing an electromechanical device, by poling an electroactive ceramic, laser machining the ceramic into a desired shape, and incorporating the ceramic into an electromechanical sensor or actuator. The laser machining may include, for example, machining grooves or slots in the ceramic, which may serve to render the properties of the ceramic anisotropic. The sensor or actuator may be a substantially planar, stress-relieved transducer. The electroactive ceramic may be, for example, a piezoelectric or electrostrictive ceramic. Poling may be achieved either before or after laser machining. Small or large amounts of material may be removed by machining, for example 1%, 5%, 20%, 50%, 75%, or 90% of the electroactive ceramic. The surface area of the ceramic may be increased by 10% or more by the machining process.
In another aspect, the invention comprises an electromechanical device comprising a substantially planar electroactive ceramic having grooves defined on a surface thereon, the grooves allowing the ceramic to conform to a curved surface, for example a surface having a radius of curvature of 0.25xe2x80x3. The device may be, for example, an electromechanical sensor or actuator. Parallel grooves may allow the device to conform to a cylindrical surface, or concentric grooves may allow the device to conform to a spherical surface.
In yet another aspect, the invention comprises an electromechanical device comprising a substantially planar bimorph electroactive ceramic member. The member may have slots defined therein that allow multiplication of an electromechanical bending response of the bimorph member. The device may be, for example, an electromechanical sensor or actuator. The slots may be substantially concentric, substantially parallel, or in any other suitable geometry.